Excavation tools of the types described herein are typically mounted to conventional excavators of the type having a backhoe, or mounted to a conventional loader with a pair of boom arms. The backhoe version includes a dipper stick, and the tool is mounted on the outboard end of the dipper stick. The loader version would include boom arms of wheel loaders, crawler loaders and skid steer loaders where the tool is mounted to the outboard end of the boom arms. These tool types are employed for excavation of medium packed substrate, e.g. substrate between the category of loose soil or loose gravel and the category of substrate requiring a ripper or hammer. Medium packed substrate does not usually require special tools or rippers to be excavated; however, conventional buckets that have teeth horizontally aligned do not excavate efficiently. Loose soil or gravel can be excavated with a conventional bucket, but a conventional bucket is generally not efficient in hard packed substrate. Solid rock excavation generally requires a hydraulic hammer, but a hydraulic hammer is not efficient for excavating hard packed substrate because it is slow and requires an additional bucket to remove the material. Intermediate substrate excavation generally requires a ripper, but a ripper may not be efficient for excavating hard packed substrate because it requires an additional bucket to remove the material. Intermediate substrate excavation also generally requires a ripper bucket combination, e.g., similar to that described in Horton, U.S. Pat. No. 7,322,133, entitled “Multi-Shank Ripper”, the complete disclosure of which is incorporated herein by reference, but a ripper bucket combination is considerably more expensive and may not be efficient for excavating hard packed substrate because it generally has a small capacity and it is not flat on the bottom for easily forming flat trench bottoms. Excavation projects generally require that the bottom of the excavated hole or trench be flat. Attempts have been made to develop tools that are effective, inexpensive, and efficient in excavating hard packed substrate while making the trench bottom flat. Simply stated, there has been one general approach, i.e. the spade nose bucket approach, e.g. as described in Evans et al., U.S. Pat. No. 5,992,062, entitled “High Penetration Bucket Arrangement,” and replaceable versions, e.g. as described in Grant, U.S. Pat. No. 7,266,914, entitled “Wear Plate Assembly,” and versions thereof, the complete disclosures of which are incorporated herein by reference. Evans et al. describes a forward center tooth that makes penetration engagement with the soil prior to the side teeth and side teeth assemblies that will engage the material at the same time. This arrangement provides for good penetration and efficiency when the first center tooth engages; however, as soon as the two outer tooth assemblies engage with the soil, the efficiency drops and the soil resistance becomes dramatically higher. Grant also described a spade nose type bucket for a loader; however, the front leading edge contains a replaceable spade nose wear portion. This design also provides good penetration when the first center tooth engages; however, as soon as the subsequent multiple side teeth engage, the efficiency drops dramatically as the teeth engage in pairs. These teeth also align with each other when viewed from the side. Each of these approaches has been found to have drawbacks.